[FFmpeg-user] V360 filter

[Paul B Mahol]

On 9/12/19, Michael Koch <astroelectronic at t-online.de> wrote:
> Am 12.09.2019 um 14:05 schrieb Paul B Mahol:
>> On 9/12/19, Michael Koch <astroelectronic at t-online.de> wrote:
>>> Paul,
>>>
>>>>>> Make this correction:
>>>>>>
>>>>>> new_fov = 180 * tan(fov/4)
>>>>>>
>>>>>> where fov the the field of view you get from the command line, and
>>>>>> fov_new is the value that you use for the filter.
>>>>>> You must exclude values too close to 360°, because 360° stereographic
>>>>>> projection is impossible.
>>>>>>
>>>>> P.S. of course fov must be converted to radians before using tan():
>>>>>
>>>>> new_fov = 180 * tan(fov * pi / 720)
>>>> Thanks, that cleared some stuff.
>>>> Should be fixed.
>>> Converting from equirectangular to stereographic is working fine now.
>>> Field of view is correct.
>>> But in the other direction from stereographic to equirectangular the
>>> output is wrong.
>>> The output doesn't contain any no-data areas. I mean those areas that
>>> aren't visible in the stereographic input. These areas should be filled
>>> with black (or better a user-defined color).
>> That is not doable by design.
>
> What about fisheye input and output?
> Fisheye (180°) input is almost the same as already implemented as
> dfisheye, and if the second hemisphere doesn't exist it can be replaced
> by a color.
> Fisheye input and output is important. For example I've made a long-time
> timelapse from many fisheye images, but some of the images require a few
> degrees tilting. That means the fisheye image must be converted to
> equirectangular, tilted, and then converted back to fisheye.

I'm working on dual fisheye output....

>
>>
>>> Also, the default output size should be width/height=2, but it is
>>> quadratic.
>> output size for what?
>
> The equirectangular output image should have width/height=2 by default.

Will try to fix it.

>
> Question:
> If the input format is stereographic and the output format is
> equirectangular, what's then the meaning of the h_fov and v_fov parameters?
> Do they define the field of view of the stereographic input (that would
> make sense),
> or do they define the field of view of the equirectangular output (that
> makes no sense, because equirectangular should always be 360° x 180°).

They are always used only for output when they make sense, for flat
and stereographic currently.

>
> Michael
>
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